Lab Exercise #12 1
Laboratory #12: RF Amplifier Design – Input/Output matching
I. OBJECTIVES
Design, simulate, and test a matched input and output biased RF transistor for use as an amplifier
with proper isolation of the DC and RF signal paths. Determine the S-parameters and compare
to the simulations.
II. INTRODUCTION
Impedance matching can readily be performed between 50 Ω generators or loads and arbitrary
complex impedances. Impedance matching to the input or output (base and collector) of an RF
transistor is no different. Given certain bias conditions, the S-parameters for the transistor are
specified in the data sheets. Therefore, the standard impedance matching techniques using
conjugate matching for maximum power transfer can be used.
Using Berner Smith Chart and Ansoft Designer SV, input and output matching networks can be
designed.
A straightforward way to achieve matching with lumped parameters is the circuit shown in
Figure 1
The capacitors CB1 and CB2 are RF shorting capacitors with values in the order of 1 µF.
The resistors R1 and R2 form the fixed bias configuration for the MRF581A RF transistor. C1
and C2 are DC blocking capacitors of 1 µF which should not significantly affect the input and
output characteristics of the amplifier. C3 is a DC bypass capacitor for noise reduction and is
typically in the order of 0.1-1 µF.
By biasing the MRF581A according to the measured specifications sheet’s S-parameter DC
conditions, appropriate amplifier S-parameters can be achieved. For the MRF581A, the S-
parameters over frequency are specified at VCE = 10V and IC = 50 mA bias.
The amplifier circuit will be constructed on SurfBoards®. Use lumped parameter resistors,
inductors, and capacitors.
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